Business and private use?
The employee can use their smartphone, tablet or laptop both for business and for private use. They are in that case also able to take their devices back home. If your employee profits from his phone in private, doesn’t matter anymore for the tax authorities. You don’t have to show that benefit as salary and you can provide the telephone without any problems. Under the old laws, you still had to show this as part of the salary, but not anymore.
A condition for the necessity criteria is that you as the employer must pay the costs. You are not allowed to give this over to your employee. However, you are able to ask for a contribution if the employee chooses for a more expensive model than needed. The phone is then officialy owned by the company. If the employee decides to leave the company, they must pay the residual value of the phone or give the phone back to the company. That is easily sorted at the end of a contract, but also if they receive a new function within the company.
The necessity criteria doesn’t only apply for phones, but also for other types of devices such as: desktops, laptops and tablets. You are able to provide your employee with several devices, without this having an effect on the tax laws.